Oups. I forgot to mention that nothing else is connected to the TV set. The cable box and the TV are connected via a Munster HDTV cable. Component cables are not hooked up.
I have had this TV for about two months. It receives its HD cable signal signal via a Scientific Atlanta Explorer 4250HD box. The box was bought at the same time as the TV. Everything has been fine up to about a week. Now I keep getting a "Searching for Signal" message most of the time when I change channels. Sometimes I can change channels without getting the message. There doesn't seem to be a pattern. Also sometimes the picture will be smaller for no apparent reason. This smaller picture is in the middle of the screen. A few minutes later the picture will be full screen again.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic